https://leetcode.cn/problems/permutations-ii/
class Solution {
public:
    vector<vector<int>>  ret;
    vector<int> path;
    bool check[9]; 

    void dfs(vector<int>& nums,int pos)
    {
        if(pos==nums.size())
        {
            ret.push_back(path);
            return ;
        }

        for(int i=0;i<nums.size();i++)
        {
            //选
            if(!check[i]&&(i==0||nums[i]!=nums[i-1]||check[i-1]))
            {
                path.push_back(nums[i]);
                check[i]=true;
                dfs(nums,pos+1);
                //不选,回溯
                check[i]=false;
                path.pop_back();
            }

        }
    }

    vector<vector<int>> permuteUnique(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        dfs(nums,0);
        return ret;
    }
};